Batteryless sensors, which harvest ambient energy as alternative power sources for long-term self-supplied operation, can have promising potentials for biomedical and wearable applications. Among various energy sources, thermal heat can provide an important energy source for implantable and wearable sensors because thermal heat can be easily accessible from the human body. However, due to constraints on thermoelectric generator (TEG) physical dimensions and a limited temperature difference between the human body and the environment, a TEG usually exhibits sub-mW output power and low output voltage (e.g., ranging from a few hundred millivolts) which cannot be directly utilized to power electronic circuits. In addition, to achieve full energy autonomy, a self-start-up function is effective to kick start system operation from a cold-state. Therefore, major design challenges in a thermoelectric energy harvester system include designing a low voltage self-start-up circuit and a high efficiency boost converter for a low voltage power source.
Different approaches have been reported to achieve low start-up voltage of TEG energy harvesting by utilizing Micro-electro-mechanical Systems (MEMS) mechanical switch, transistor threshold voltage trimming, off-chip transformer and auxiliary LC oscillator to kick start a boost converter operation. However these approaches require external motion force to trigger start up, large system size, or increased fabrication cost or may lack a shut-down mechanism for an electrical start-up circuit leading to leakage current causing significant efficiency degradation during a normal operation mode.
Thus, what is needed is a method and device for energy harvesting to provide an efficient solution to minimize power consumption of the start-up circuit during system steady-state operation by automatic disabling the start-up circuit during steady state operation. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.